c-myc DNA breaks and c-myc-IgH locus translocations: roles of AID and oxidation

描述(由申请人提供)：抗体(免疫球蛋白，Ig)类别转换使B淋巴细胞从产生IgM转换为产生Ig G、Ig A或Ig E，从而提高抗体清除体内病原体和细菌毒素的能力。类别转换是通过染色体内DNA重组事件发生的，必须仔细控制，以避免与其他染色体的异常重组(易位)。然而，偶尔也会发生移位。有时，由于免疫球蛋白基因移位到编码癌基因的染色体位置，例如c-myc，导致c-myc基因的异常表达，从而导致B淋巴瘤或骨髓瘤。本申请旨在研究DNA双链断裂(DSB)如何被引入小鼠c-myc基因，以及激活诱导的胞苷脱氨酶(AID)在c-myc-IgH易位过程中的作用。在目标1中，我们将研究一种假说，即活性氧物种(ROS)引起DNA损伤，导致c-myc基因的DSB，并刺激AID的脱氨活性，因为脱氨是通过氧化反应发生的。在目标2中，我们将调查AID是否有除脱氨酶活性之外的额外活性，从而导致c-myc-IgH易位。在目标3中，我们将研究AID C末端的10个氨基酸的作用，它是类切换重组所必需的，但不是体细胞超突变所必需的，并且已被证明抑制c-myc-IgH易位。我们将检验一种假设，即参与开关重组的DNA修复蛋白是由C末端招募的。 公共卫生相关性：该项目调查了引发B细胞淋巴瘤和骨髓瘤发生的事件。我们将研究当正常的小鼠B细胞被诱导经历正常的抗体类别转换以响应激活信号时，DNA断裂是如何引入c-myc癌基因的。这些DNA断裂可导致c-myc癌基因易位到免疫球蛋白(Ig)重链基因座，从而增加c-myc基因的表达，从而导致细胞转化和恶性转化。我们将研究在抗体类别转换过程中启动IgH基因DNA断裂形成所需的蛋白质(激活诱导胞苷脱氨酶，AID)是否需要将DNA断裂引入c-myc基因，以及AID是否具有导致IgH基因和c-myc基因之间易位的额外作用。我们还将研究AID本身在正常类别转换过程中的功能，因为这会影响c-myc基因和IgH基因之间的易位。

DESCRIPTION (provided by applicant): Antibody (immunoglobulin, Ig) class switch causes B lymphocytes to switch from producing IgM to producing IgG, IgA or IgE, which improves the ability of the antibody to remove pathogens and bacterial toxins from the body. Class switching occurs by an intrachromosomal DNA recombination event that must be carefully controlled in order to avoid aberrant recombination with other chromosomes (translocations). However, occasional translocations do occur. Sometimes they result in B lymphomas or myelomas due to translocations of the Ig genes to a chromosomal site encoding an oncogene, e.g. c-myc, which induces aberrant expression of the c-myc gene. This application proposes to investigate how DNA double-strand breaks (DSBs) are introduced into the mouse c-myc gene and the role of activation-induced cytidine deaminase (AID) in the process of c-myc-IgH translocations. In Aim 1, we will investigate the hypothesis that reactive oxygen species (ROS) induce DNA lesions that lead to DSBs in the c-myc gene, and also stimulate the deamination activity of AID, as deamination occurs by an oxidation reaction. In Aim 2, we will investigate whether AID has additional activities besides its deaminase activity that contribute to creating c- myc-IgH translocations. In Aim 3, we will investigate the role of the 10 amino acids at the C terminus of AID, which is required for class switch recombination but not for somatic hypermutation, and has been shown to repress c-myc-IgH translocations. We will examine the hypothesis that DNA repair proteins involved in switch recombination are recruited by the C terminus. PUBLIC HEALTH RELEVANCE: This project investigates the events that initiate the generation of B cell lymphomas and myelomas. We will study how DNA breaks are introduced into the c-myc oncogene when normal mouse B cells are induced to undergo the normal process of antibody class switching in response to activation signals. These DNA breaks can result in translocations of the c-myc oncogene to the immunoglobulin (Ig) heavy (H) chain gene locus, which increases expression of the c-myc gene, and this can lead to cell transformation and malignancy. We will study whether the protein that is required for initiating DNA break formation in the IgH genes during antibody class switching (activation-induced cytidine deaminase, AID) is required for introducing DNA breaks into the c-myc gene, and whether AID has additional roles that lead to the translocations between the IgH genes and c-myc genes. We will also investigate the function of AID itself during normal class switching, as this affects translocations between the c-myc gene and the IgH locus.